Abstract: J44.00001 : A closer look at the two-layer model

Author:

Dongdong Peng(Boston University)

Previously we have measured the viscosity of short-chain, unentangled
polystyrene films coated on silicon covered with a 100 nm thick oxide layer.
We found that a two-layer model, portraying the films as being made of a 3
nm thick mobile layer sitting on top of a bulk-like inner layer, was able to
describe our data very well. More recently, we extended similar measurements
to entangled films with a higher molecular weight of 212 kg/mol. We found
that the same two-layer model was able to describe the viscosity
measurements, but would imply an unphysically large stretching of the
polymer chains in the films or else the near-surface chains would have to be
oblate spheroids with an aspect ratio of about 4. In this talk, I will
discuss new results we obtain from films with higher molecular weights of up
to 2316 kg/mol and also films that are deposited on a different kind of
substrate, namely hydrogen terminated silicon. Implications of these results
on the two-layer model will be discussed.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.J44.1